1. Field of the Invention
The invention relates to the delivery of implants within body vessels and more particularly to mechanisms for selectively releasing stents and other expandable vascular implants.
2. Description of the Related Art
Vascular disorders and defects such as aneurysms, embolisms, and other arteriovenous malformations are especially difficult to treat when located near critical tissues or where ready access to a malformation is not available. Both difficulty factors apply especially to cranial aneurysms. Due to the sensitive brain tissue surrounding cranial blood vessels and the restricted access, it is very challenging and often risky to surgically treat defects of the cranial vasculature.
Alternative treatments include vascular occlusion devices such as stents and embolic coils deployed using delivery catheters having a distal end positioned at an occlusion or aneurysm. Several types of stent delivery systems are disclosed in U.S. Patent Publication No. 2005/0049670 by Jones et al., for example.
In a currently preferred procedure to treat a cranial aneurysm, the distal end of an embolic coil delivery catheter is inserted into non-cranial vasculature of a patient, typically through a femoral artery in the groin, and guided to a predetermined delivery site within the cranium. A number of delivery techniques for vaso-occlusive devices, including use of fluid pressure to release an embolic coil once it is properly positioned, are described for example by Diaz et al. in U.S. Pat. Nos. 6,063,100 and 6,179,857.
Often, before embolic coils are implanted, a stent-like vascular reconstruction device is first guided beneath the aneurysm using a delivery catheter. One commercially available reconstruction product is the CODMAN ENTERPRISE® Vascular Reconstruction Device and System as described, for example, in a Navigate Tough Anatomy brochure Copyright 2009 by Codman & Shurtleff, Inc., 325 Paramount Drive, Raynham, Mass. The CODMAN ENTERPRISE® device is carried by a central delivery wire and initially held in place on the delivery wire in a collapsed state by a sheath-type introducer. Typically, a delivery catheter such as a PROWLER® SELECT® Plus microcatheter, also commercially available from Codman & Shurtleff and as disclosed by Gore et al. in U.S. Pat. No. 5,662,622, for example, is first positioned intravascularly with its distal tip slightly beyond the neck of the aneurysm. The tapered distal tip of the introducer is mated with the proximal hub of the delivery catheter, and the delivery wire is then advanced through the delivery catheter.
The CODMAN ENTERPRISE® device has a highly flexible, self-expanding closed cell design with a number of radiopaque markers at each flared end of the device, similar to the stent illustrated in the published patent application by Jones et al., cited above. After the device is properly positioned and allowed to expand against the parent vessel, one or more embolic coil delivery catheters can be threaded through one of the cells of the expanded device and then into the aneurysm to place embolic coils therein.
The CODMAN ENTERPRISE® device can be partially deployed and recaptured once by carefully manipulating the delivery catheter relative to the central delivery wire to allow the distal portion of the device to expand while retaining the distal tip of the delivery catheter over the proximal portion of the device. This action continues to trap the radiopaque markers at the proximal end of the device within an indentation formed in the delivery wire. However, if the delivery catheter is withdrawn even slightly past the indentation, the CODMAN ENTERPRISE® device will become fully expanded and cannot be recaptured or repositioned by the delivery system.
A number of well-known stent delivery systems, for both self-expanding and mechanically expanding stents, are described by Ravenscroft in U.S. Pat. No. 5,702,418, for example. Partial deployment and retraction of a stent is identified as an important criterion to enable a physician to recover a stent that is not initially deployed in a proper position.
A delivery system having a weak, non-marring inner sheath and a stronger outer sheath is disclosed by Vrba et al. in U.S. Pat. No. 6,254,609. Another delivery system utilizing inner and outer sheaths is disclosed by Ruetsch in U.S. Pat. No. 7,175,650.
Alternative mechanical detachment systems for placing an endoluminal implant, while resisting kinking, are described by Hijlkema et al. in U.S. Patent Publication No. 2010/0063573. An outer slidable sheath has an advanced position covering an implant and a retracted position which exposes the implant. In one aspect, at least one of the proximal end of a catheter tip or a stabilizer distal end forms a docking section which releasably engages a portion of the implant when the outer sheath is withdrawn proximally past the docking section. Each docking section has an engagement geometry with a flared engagement surface or a pocket with a bottleneck geometry. In another aspect, an inner tubular member with one or more flexible fingers engages the implant when the sheath is in the advanced position. Again, the outer sheath is retracted to deploy the implant.
Stent-like, generally non-deployable devices are also utilized to treat disorders arising from embolisms and atherosclerosis. An embolism is the sudden obstruction of a blood vessel by blood clots, cholesterol-containing plaques, masses of bacteria and other debris. A blood clot which obstructs a blood vessel is also referred to as a thrombus. If the embolic obstruction occurs in the brain, it can cause a sudden loss of neurological function referred to as a stroke, in particular an acute ischemic stroke.
A number of devices for treating embolic strokes and atherosclerotic deposits are described for example in U.S. Pat. No. 5,972,019 by Engelson et al. Other, more recent neurological devices include the Micrus Revasc™ of Codman & Shurtleff, Inc., the Solitaire™ device of Microtherapeutics, Inc. d/b/a ev3 Neurovascular, and the Trevo™ and Merci Retreiver™ devices from Concentric Medical.
It is therefore desirable to have an improved implant delivery system which retains flexibility during insertion to treat a vascular malformation yet decouples implant release from retraction of a delivery catheter.